Urinary Biopyrrin Levels and Their Relationship with the Menstrual Cycle and Concomitant Symptoms Among Healthy Nonpregnant Women of Reproductive Age: A Cohort Study.

Background: Urinary biopyrrin (UBP) is an oxidative metabolite formed from the reaction of bilirubin with reactive oxygen species. Previous studies have explored the relationship between UBP levels and certain diseases or pregnancy. However, UBP levels in healthy nonpregnant women have not been well examined. We aimed to clarify the representative value of UBP in healthy nonpregnant women and explore its relationship with menstrual cycles and concomitant symptoms.

Methods: We included healthy, nonpregnant Japanese women aged 20-39 years with normal body mass index and menstrual cycle. In total, 1260 urine samples collected during 43 menstrual cycles of 36 women were analyzed to determine the representative values and reference intervals of UBP levels. The correlation between daily UBP levels and the order of the day was explored, and median UBP levels of 5-day clusters were compared using Friedman and Mann-Whitney U tests. These analyses were also conducted in women with concomitant symptoms during the menstrual cycle.

Results: The median UBP level in all samples was 0.2291 (reference: 0.0102-2.9335) μmol/gCr. There was no significant relationship between the median UBP level and menstrual cycle, regardless of the presence of self-manageable symptoms during or before menstruation.

Conclusions: The representative UBP value and its reference interval can serve as standards for comparison with other populations. Our findings suggest that the UBP level may be an objective oxidative stress indicator that is less sensitive to menstrual cycle and concomitant symptoms. UBP levels in healthy nonpregnant women could be assessed regardless of the menstrual cycle and concomitant symptoms.